The 15-block puzzle is often referred to (incorrectly) as Sam Loyd's 15-Puzzle (see Slocum and Sonneveld). The actual inventor was Noyes Chapman, the postmaster of Canastota, New York, who applied for a patent in March 1880.

From Dan Hoey (Nov 10 2003): The set of moves from a given position depend on where the blank is. There is also a variant in which sliding a row of tiles counts as a single move. For the 8-puzzle I find: